Composting is a type of aerobic waste treatment process. It is a process by which organic matter is broken up through micro-organisms and leads to an end product “compost” which can be used for soil improvement or as fertiliser. It is one approach to deal with organic waste accruing in households or in industrial production, e.g. meat or fish processing. Known approaches for the disposal of organic waste are waste incineration or land filling. In the past few years, the legislature has required that organic waste must be treated prior to disposal in landfills or incineration. Aerobic waste treatment systems have been known for a long time and can be found in small scale versions, e.g. as compost heaps in gardens, or as large scale industrial composting sites. The composting system can also be used to decrease the volume of waste material prior to land filling. Another type of aerobic waste treatment system involves soil remediation.
The increasing world population leads to the creation of more waste matter, including organic waste. More people require more food and there is therefore also an increasing requirement for soil improvement and fertilisers, such as compost.
Aerobic waste treatment processes such as composting, organised as businesses, need to maximise their profit. Commercial operators receive—usually from local authorities or from the waste producers themselves—their income from gate fees for disposing of the waste. The operators can also sell the end product as a fertiliser. Maximisation of their profit comes from optimising the through-put of the waste treatment process, increasing the amount of compost produced and improving the quality of the compost. This is achieved by providing the micro-organisms with the best possible environment to break down the organic waste.
For the operation of industrial aerobic waste treatment sites, both stationary and portable composting systems are known in the art. Both of these types of industrial aerobic waste treatment systems have to provide for emission reduction through minimisation of dust, bio-aerosol and odour. The industrial composting sites have to be adapted to large quantities of organic waste while keeping cost as low as possible. For economically efficient operation of the industrial composting site, the time required to set up the composting system has to be kept short. This is particularly important for transportable composting systems to keep the downtime of the composting system low. It is therefore desirable to provide for an easy transportation of parts and a quick set-up of the portable composting systems.
Typical stationary industrial systems such as shown in FIG. 5 for outdoor composting comprise an aeration system, a control unit and a flexible (textile) enclosure. They often also comprise a massive concrete wall. A power shovel heaps organic waste against the massive concrete wall and this wall is therefore known as a “push wall”. This procedure allows the efficient handling of large amounts of organic waste. Deployment mechanisms for the deployment of covers over the waste heap are often arranged on the concrete wall to provide a minimum height for the cover handling with minimum mechanical stress to the covers. The arrangement of these deployment mechanisms can be difficult and take a lot of time, particular when only limited equipment is available and when weather conditions are unfavourable. Only one side of the push wall can be used to heap the organic waste against, as ventilation and control equipment is placed on the other side of the push wall.
The push wall may also serve for other purposes not related to the heaping of the organic waste. For example, the push wall can act as a fence or screen the composting site from view.
The set-up of such a stationary composting site involves costly and time-consuming construction work, such as the preparation of foundations and concreting. There may also be a requirement to obtain planning permission from the local authority which can be time-consuming and expensive. The stationary composting site described above is obviously not portable which means that it cannot be moved from site to site as the need arises. As a result, a substantial investment in capital equipment must be made which is lost should the site be moved to other premises.
In the UK patent GB-A-1502217 an apparatus and method is taught which states that the necessary investment and the operational costs are reduced by a composting system for composting very large amounts of waste in a simple and economical manner. The composting system of the '217 patent is a stationary composting system and comprises two side walls between which the composting takes place. To access the compost there are openings from both sides of the compost heap. The compost is stacked between two parallel walls of the compost heap. The compost is positioned and taken out from the side openings. The parallel side walls do not act as walls against which the compost can be heaped with a power shovel. The composting system of the '217 patent therefore does not have a push wall.
The UK patent GB-A-1597354 deals with the problems of temperature distribution in compost heaps. There is no indication in the '354 patent that the composting system is movable. A low partition wall is, in one of the taught embodiments, an integral part of the stationary composting system of the '354 patent and thus the low partition wall is also not movable. The low partition wall separates compost in different composting states. However, the compost is heaped higher than the low partition wall and therefore the low partition wall is not a push wall. It is stated in the '354 patent that it is necessary that the free surface of the waste material is in free contact with atmospheric air, thus no cover of the waste is present.
Portable composting systems are known both as outdoor and indoor solutions. The U.S. Pat. No. 6,383,803 (portable composition system with reconfigurable air flow) describes an assembly of an air blower, a suction manifold, a discharge manifold, and ventilation (pile) manifolds which can be transported to a composting site and set up. Compost heaps can be equipped with the ventilation manifolds for a controlled aeration of the compost heaps.
Portable composting systems are also known as home appliances. The UK patent GB-A-1427331 describes such a household composting system. In the '331 patent, as normally in household composting systems, the compost is surrounded by the composting system. As the compost is usually manually deposited in the compost bin there is no need for a push wall to absorb the load of a power shovel pushing the compost against the push wall or for absorbing the load of a compost heap which is several metres high.
The heaping up of organic waste on a planar field, as shown in FIG. 1 of U.S. Pat. No. 6,383,803, is much less effective and more time-consuming than heaping the organic waste against a push wall. The use of the push wall leads to increased space efficiency (i.e. more volume of waste can be processed in the same area).
The German patent DE-C-3209565 describes a portable composting system which increases space efficiency. The compost is heaped up within three walls. The three walls comprise two parallel side walls and a front wall, together forming a U-like shape. Within the area defined by the composting system the compost is heaped up and the waste is pressed together in the composting process under the own weight of the waste. The three walls can be slid away in order to allow recovery of the waste. The described system of the '565 patent is less efficient than typical stationary composting systems as the waste has to be inserted in the composting system from the open side of the composting system. Thus the operating area for a power shovel is reduced. The described construction of the composting system of the '565 patent is a very light weight composting system, preferably made of metal grids. This construction allows pressing together of the waste under the own weight of the waste. However, such a described light-weight system is not adapted to pushing the waste in the composting system against the walls with a power shovel.
Portable composting systems can also be designed as indoor systems. To protect the environment and to provide stable process conditions the compost is processed within a closed container. A mobile modular system for composting making use of freight containers is known. The German patent DE-C-198 33 624 (processing of organic waste material) teaches an assembly of modules containing a mobile processing container. The organic waste is reduced in the container to a substrate for further processing or for deposition at a dump. The equipment for the composting process comprises a modular assembly which is used to conduct the process stages of initial aeration, anaerobic fermentation, water removal and drying within a mobile processing container. This processing container is termed a bio select percolator (BSP). The processing container comprises energy and supply facilities for the composting process. In a preferred embodiment the BSP is a modified standard 20 foot freight container. Note that although the original document says 20 inch freight container it is clear from the context that a 20 foot freight container is meant. The freight container is equipped with transport hooks, a system for active water extraction and for suction ventilation, perforated side walls, a base for a passive water extraction and a pressure ventilation system.
As the composting process is carried out within the 20 foot freight container, the system described in this German '624 patent is not adapted to large scale composting as desired in outdoor systems. The volume of organic waste composted is limited by the freight container volume. The manufacturing costs for the compost exceed the manufacturing costs for compost produced by outdoor composting systems.
The German patent applications DE-A-19724462 and DE-A19930223 also describe composting within closed containers. Therefore similar problems occur, as already described with respect to the '624 patent, such as the limited volume available for composting. It is difficult to get the waste into the container as there is only the small opening on one side. The '426 patent application teaches a second composting of already composted material. The '426 patent application suggests a high stacking of the compost outside the composting system. The stacked compost is then transported into the composting system. There is no push wall described in the '426 patent application and the compost should be stacked higher than the container for the second composting, thus needing mechanical tools for piling up the compost.
There is also no push wall described in the '233 patent application, as the described composting system is an in-vessel composting method. The '233 patent application describes a closed container. There is no clear teaching how the waste is filled into the closed container. However the description suggests filling the container from the top.
The U.S. Pat. No. 4,146,382 describes a system which forms tunnels in the compost heap to allow an improved air circulation through the compost heap. No push wall is described in the '382 patent against which waste is or could be pushed, e.g. by a power shovel. The process of heaping up the compost shows the similar inefficiencies as already discussed with respect to the '803 patent.
A way of dealing with problems arising from emissions as dust, bio-aerosols and odour in outdoor systems and also a way to provide a more stable process environment is the use of covers for covering the outdoor compost heap. By enclosing the compost with a cover a method for an outdoor in-vessel composting is provided. The covers can be air permeable or air impermeable. There are different systems known for composting which employ covers over the compost heap. For example the European patent application EP-A-0 863 856 describes a composting system having an area for containing a mass of compostable material and a weatherproof cover. The weatherproof cover can be conformable to the mass of compostable material and protects the compostable material from environmental factors. The weatherproof cover defines a composting environment in which environmental conditions may be controlled during the composting process. The weatherproof cover is air impermeable according to the description of this patent application.
In the German patent DE-C-42 31 414 an air permeable cover material for compost heaps is described. The cover described in DE-C-42 31 414 comprises an air permeable but water impermeable membrane.
No reference is made in the documents EP-A-0 863 856 and DE-C-42 31 414 to the use of a push wall which would increase the efficiency of the composting site.
One of the problems with covers for aerobic waste treatment systems is the size of the covers. Large organic waste heaps require substantial covers which can no longer be easily moved because of their weight. It is technically possible to construct a large cover out of many smaller pieces being joined together. This requires additional time and effort. Therefore large covers are preferably used for industrial aerobic waste treatment. Large covers can only be handled easily if a mechanical deployment apparatus is used. The deployment apparatus works best if placed at a level higher than the top of the waste heap as this avoids mechanical stress due to resistance between the cover and the waste heap. Therefore the deployment apparatus is mounted on the push wall against which the organic matter is heaped. A static concrete push wall cannot be moved from site to site and therefore is an unsuitable investment for temporary operations. As a result the combination of a movable push wall allowing the use of a high mounted deployment apparatus for easy handling of the large cover is an optimal technical and economically most efficient aerobic waste treatment system.